This invention relates to implementing control features on an integrated circuit (IC). In particular, this invention relates to implementing a control feature on an IC without adding a dedicated pin to implement that feature.
The invention is described below as it applies to a charge pump circuit; however, persons skilled in the art will appreciate that the principles of the present invention can be applied to other integrated circuits as well. By enabling additional control features to be added to an IC without adding extra pins, the invention preserves valuable space on the circuit board.
Direct current to direct current (DC--DC) conversion circuits can be implemented using an inductor based topology or a capacitor based topology (e.g., a charge pump). Each type of converter topology has its own advantages and disadvantages. The inductor based topology requires fewer power switches and can be implemented in fewer pins than the capacitor based topology. For example, a conversion circuit that boosts voltage four times (a quadruplet) can be implemented with an inductor based topology using three pins, while a capacitor based topology requires a minimum of eight pins.
The inductor based topology, however, also has several disadvantages. These circuits are more complex to design than capacitor based topologies because they require numerous external components in addition to many internal IC controls. Moreover, they require magnetic energy storage, which often is difficult to stabilize and radiates EMI waves.
Capacitor based topology requires a minimum of eight power switches and eight pins to operate. Adding a control feature will normally increase the pin count to at least nine pins. To avoid increasing pin count and consuming additional space on the circuit board, the present invention enables the designer to add a control feature to the IC without requiring additional pins be added to the IC.